Charged with Meaning

The further you delve into the physics of electronics and materials, the more you will hear about the importance of electric charge. What charge particles have determines much of how they interact with other particles. In materials many of the electronic and magnetic effects are, at a basic level, due to charge. So what is it?

Electric charge is a fundamental property of matter. How much charge a particle has determines the force it will experience from an electromagnetic field, and such a field can be generated either by other charged objects or by the motion of magnetic objects. This is similar to mass, which is another fundamental property that determines the gravitational force an object will experience as it interacts with other massive objects. There is one key difference between charge and mass, however: there are two types of charge, positive and negative, whereas mass can only be positive (or zero). From the particle perspective, we can have particles like protons that have a positive charge, particles like electrons with a negative charge, and particles like neutrons that have no charge. Anything with a charge creates an electromagnetic field, and other charged particles nearby will feel a force from that field.

Now, say that we have two particles sitting near each other. Each one will have an associated electromagnetic field, and the total field will be a sum of the individual fields. The size of the electromagnetic force experienced by each particle due to the other depends on the magnitude of the two charges. But whether the charge on each particle is positive or negative is important for the following two reasons:

Similar charges repel.

Dissimilar charges attract.

So with our two particles, if they both have positive charge, or they both have negative charge, they will each feel a force directed away from the other charge. But if one is negatively charged and one is positively charged, they will experience the same size force toward each other. This force is part of what holds atoms together. Protons and electrons have equal and opposite charge. In atoms, we have a nucleus of protons and neutrons surrounded by a cloud of electrons. If there are more protons than electrons, the atom as a whole will be positively charged and will be attractive to nearby electrons. But if there are more electrons than protons, the atom is instead negatively charged, and the electrons within it are not as strongly bound.

We can already see that the charge of a particle is extremely important on the atomic scale. As we look at collections of atoms, the interactions will get more complicated, but the pieces to remember are:

Charge is an inherent property of matter.

Charged objects create an electromagnetic field.

How strong a force an object feels from such a field is determined by that object’s charge.